Opal: Nature's Fireworks
The History
Mysterious opals contain the wonders of the skies- sparking rainbows, fireworks, and lighting - shifting and moving in their depths. Opal has been treasured throughout history around the world. Archaeologist Louis Leakey found six-thousand year old opal artifacts in a cave in Kenya!
Roman historian Pliny described the beauty of opal as the combination of the beauty of all other gems: "There is in them a softer fire than the ruby, there is the brilliant purple of the amethyst, and the sea green of the emerald- all shining together in incredible union. Some by their splendor rival the colors of the painters, others the flame of burning sulphur or of fire quickened by oil."
Opal was much loved and valued highly by The Romans, who called it opalus. At the same time, opal was also sought in what would become the Americas. The Aztecs mined opal in South and Central America.
Opal was also treasured in the Middle Ages and was called ophthalmios, or eye stone, due to a widespread belief that it was beneficial to eyesight. Blonde women wore opal necklaces to protect their hair from losing its color. Some thought the opal's effect on sight could render the wearer invisible. They were recommended for thieves!
Opal as Muse/
Opals are also set in the crown jewels of France. Napoleon gave Josephine a beautiful opal with brilliant red flashes called "The burning of Troy," making her his Helen.
Shakespeare found in the opal a symbol of shifting inconstancy, likening play of color to play of mind in one of the most apt uses of gemstone symbolism in literature. In Twelfth Night, he writes: "Now the melancholy God protect thee, and the tailor make thy garments of changeable taffeta, for thy mind is opal."
In the nineteenth century, opal was considered unlucky due to the plot of a popular Sir Walter Scott novel of the time. The heroine of the novel has her life force caught in the beautiful opal she wears in her hair and she dies when the fire in the opal is extinguished.
Queen Victoria loved opals and often gave them as wedding presents. She and her daughters created a fashion for wearing opal. Queen Victoria was one of the first to appreciate opals from an exciting new source: Australia.
Ancient opal came from the mines near Cervenica, Hungary, in what is now Eastern Slovakia, where hundreds of men mined the stone. Ancient opal fanciers never had the chance to see the opal of Australia, where the opal of today was born, which far surpasses the beauty of Hungarian opal in fire and brilliance.
A Gem of Water, Born in the Desert
The story of opal in Australia begins more than 100 million years ago when the deserts of central Australia were a great inland sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 millions years ago released a lot of the silica into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of this silica became precious opal. Opal is one of the few gemstones that is sedimentary in origin. Opal still contains 6 to 0 percent water, a remnant of that ancient sea.
Gold panners in Australia found the first few pieces of precious opal in 1863. Mines at White Cliffs began producing in 1890.
Only opal with a perfectly aligned grid of silica spheres will show play of color, which is created through diffraction. The size of the spheres determines the wavelengths and therefore the colors seen. The brilliance of the colors is determined by the regularity of the grid.
The strength of the colors seen in opal also depends on the background body color and the transparency of the stone. The body color determines the variety of opal and has a large impact on the value.
Black opal, opal with a black to dark gray body color, has the most brilliant colors and is the most valuable. Crystal opal, the next most costly type of opal, is transparent with flashes and is highly valued due to the brilliance of its colors and the fact that many layers of color within the stone can also be seen. White and milky opals tend to have more diffused colors due to the light background color. This is the most affordable type of opal.
Another more unusual type of opal is boulder opal, which has opal with an ironstone host rock matrix which creates a natural dark background to view its fire. There sometimes occur in "splits" a matched pair of opals created when a piece of boulder opal is split is split along the opal vein. These are particularly favored for earring, since they are mirror images of each other.
Choosing an Opal
Within each opal variety, the brillance of the play of color is the most important value factor. After this consideration, the colors seen and the pattern of the colors will also influence value. Generally, opal with red fire is the most valued because opal that shows red will also show other colors when rolled back and forth: it contains the whole spectrum. The pattern of the play of color also influences value. Generally large flashes and broad patterns are more rare and valuable than small pinfire patterns.
Black opal is found only in Australia in Lightning Ridge, the most famous opal deposit in the world since it was discovered in 1903, and in Mintabie, which also produces large quantities of light opal.
Another large opal producing area in Australia is Coober Pedy, which produces light opal. The name Coober Pedy is an Aboriginal name meaning "white man in a hole." If you visit Coober Pedy, you will understand how it got its name: many houses - and even a church! - are burrows dug into the ground called dugouts. This type of dwelling is quite practical and cool as temperatures soar in the daytime.
Andamooka is known for producing crystal opal and light opal. Boulder opal is produced in several areas in western Queenland.
In addition to Australia, a small quantity of precious opal is produced in Brazil. Mexico and the state of Oregon in the united State produce a volcanic opal called fire opal. Fire opal is transparent opal ranging in color from colorless to yellow, orange, and red. Sometimes it also shows play of color in addition to its bright orange body color. Low quality opal was recently discovered in Ethiopia.
A green translucent opal that resembles chrysoprase or jade, which is called prase opal, is found in Tanzania, A beautiful blue-green opal is found in Peru in the Andes Mountains. These types of opal do not display play of color.
The hardness of opal ranges from 5.5 to 6.5 on the Mohs scale. It should be protected from heat and strong light, which can dry it out, causing cracks. Ultrasonic cleaners, metal polish, acids, and any strong solvents should be avoided. Exposed corners or points on pear or marquise shape opals may chip if hit while they are being worn. Opal is best set in a protected mounting.
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